The Special Forces trailer focuses on the symbiotic relationship between different races and classes: engineers, infiltrators, vanguards, sentinels, and straight-up soldiers.

Some are better suited to manipulating energy fields, others to stealth, while tailored load-outs allow players to tank into opposition forces -- but it's always handy to have a teammate nearby on resuscitation duty.

Such a class-based approach is now standard for many online shooters, borrowed from the role-playing genre and successfully appropriated by Team Fortress 2 and the Battlefield series as a way of encouraging players to discover the rewards of teamwork; Gears of War 3 and Modern Warfare 3 offered their own twist on the mechanic.

Mass Effect 3: Special Forces trailer - http://youtu.be/nyy5fAFw6UM
Official website - masseffect.com